NOVEL MATERIAL

Abstract

The present invention relates to a substrate comprising an ion-implanted layer, for example a cation, wherein the ion implanted layer has a uniform distribution of the implanted ions at a significantly greater depth than previously possible. The invention further comprises said substrate wherein the substrate is a silicon based substrate, such as glass. The invention also comprises the use of said material as a waveguide and the use of said material in measurement devices.

Claims

1. A substrate comprising an ion-implanted layer wherein the penetration depth of the implanted ions is at least 50 nm, or at least 200 nm.

2. A substrate according to claim 1 where the penetration depth of the implanted ions is at least 500 nm.

3. A substrate according to claim 1 wherein the ion implanted layer has a substantially uniform distribution of the implanted ions.

4. A substrate according to claim 1 wherein the ion implanted layer has an implanted ion density of at least 10.sup.21 ions cm.sup.3, or at least 10.sup.23 ions cm.sup.3.

5. A substrate according to claim 1 wherein the substrate is a glass selected from silica, silicate, phosphate, tellurite, tellurite derivatives, germanate, bismuthate and solgel route glasses.

6. A substrate according to claim 1 wherein the substrate is an optical polymer.

7. A substrate according to claim 6 wherein the optical polymer is selected from Poly(methyl methacrylate), polyvinyl alcohol, polyether ether ketone, polyethylene terephthalate, polyimide, polypropylene, and polytetrafluoroethylene.

8. A substrate according to claim 1 wherein the ion-implanted layer is either: (i) on an outside face of the substrate; or (ii) within the substrate.

9. A substrate according to claim 1 wherein the ion-implanted layer either: (i) encompasses substantially the whole area of the substrate; or (ii) comprises one or more zones.

10. A substrate according to claim 9 wherein one or more of the zones overlap.

11. A substrate according to claim 9 wherein the zones comprise the same or different ions.

12. A substrate according to claim 1 wherein the ion is a cation.

13. A substrate according to claim 12 wherein the cation is selected from the group Nd(3+), Yb(3+), Er(3+), Tm(3+), Pr(3+), Ho(3+), Sm(3+), Eu(3+), Tb(3+), Ce(3+) and La (3+).

14. A waveguide comprising a substrate according to claim 1.

15. A biosensor comprising a substrate according to claim 1 as an optical substrate or as a waveguide comprising said substrate.

16. A method for the non-invasive measurement of a metabolite in an animal which comprises: (i) applying a sensor on or near said animal, said sensor comprising an optical substrate or waveguide; (ii) irradiating said substrate or waveguide with a light source such that a portion of the light escapes into the animal; (iii) measuring the photoluminescence lifetime of the escaped light; wherein the recovery lifetime is correlated with the level of the metabolite.

17. A process for fabricating a substrate according to claim 1 comprising: ablating a target layer with incident radiation from a laser in the presence of a substrate whereby a quantity of the target layer is implanted into the substrate.

18. A process according to claim 17 wherein the target layer is tellurium glass.

19. A process according to claim 17 wherein the laser is a Femtosecond laser.

20. A process according to claim 17 wherein the substrate is heated.

21. A substrate comprising an ion-implanted layer wherein the ion implanted layer has a substantially uniform distribution of the implanted ions.

22. A substrate comprising an ion-implanted layer wherein the ion implanted layer has an implanted ion density of at least 10.sup.21 ions cm.sup.3, or at least 10.sup.23 ions cm.sup.3.

Description

[0110] The invention will now be illustrated with the following non-limiting examples with reference to the following figures.

[0111] FIG. 1shows schematically the ablation, plasma production and the multi-ion diffusion process.

[0112] FIG. 2shows the SEM and TEM images of the substrate cross sections with a highly defined and uniformly diffused region in silica at two different target ablation energies of 47 J (Sample A) and 63 J (Sample B) respectively.

[0113] FIG. 3shows a 4001600 nm HAADF slices of individual elements of Sample B.

[0114] FIG. 4 represent the Raman spectrum of ion diffused glass compared with bare silica and tellurite bulk glass.

[0115] FIG. 5 represents a schematic diagram of a biosensor, such as a glucose sensor of the invention.

[0116] FIG. 6 shows Molar absorptivity spectra of glucose (solid), alanine (dashdot-dot), ascorbate (medium dash), lactate (short dash), urea (dotted), and triacetin (dash-dot) at 37.00.1 C. over the first overtone.

[0117] FIG. 7 shows the variation in photoluminescence lifetime measured at three different wavelengths for human blood sample with varying concentrations of glucose

ABBREVIATIONS USED

[0118] HAADF high angle angular dark field elemental mapping [0119] NIR near infra red [0120] SEM Scanning electron microscopy [0121] TEM Transmission electron microscopy

EXAMPLE 1

Implantation into Silica Glass

[0122] Multi-ion diffusion into silica glass was produced via femtosecond laser ablation of an erbium doped tellurite glass target containing zinc and sodium. A Ti-sapphire femtosecond laser operating at a wavelength of 800 nm with 100 fs pulse width and a maximum repetition rate of 1 kHz (Coherent Inc, Santa Clara, Calif., USA) was used to ablate the glass target generating an expanding plasma plume consisting of multiple metal ions (multi-ion). A tellurite glass target with a molar composition of 79.5TeO.sub.2: 10ZnO:10Na.sub.2O:0.5Er.sub.2O.sub.3 produces multiple ions Te4+, Zn2+, Na+ and Er3+, which diffuse into the silica glass substrate under certain process conditions. The ablation, plasma production and the multi-ion diffusion process are schematically shown in FIG. 1.

[0123] Experiments were carried by varying the laser energy, repetition rate, target to substrate distance and finally the deposition target temperature. The deposition target was not translated for the simplicity of the experiment and for a better understanding of parameter variation along the sample surface. There was an variation in diffusion depth and refractive index profile along the surface when radially moving outwards from the centre, therefore all the characteristic properties of the modification provided were measured from the centre of the sample unless otherwise stated.

[0124] Optimum results were obtained for laser energies between 40 J-75 J when operated at 500 Hz and 1 kHz. The ablation target to substrate distance was set at 70 mm and the substrate temperature was set at 973K. FIG. 2 represents the SEM and TEM images of the substrate cross sections with a highly defined and uniformly diffused region in silica at two different target ablation energies of 47 J (Sample A) and 63 J (Sample B) respectively. Diffusion depths of the ions increased from 350 nm to 850 nm with laser energy while the deposition time was 6 hours and repetition rate was 500 Hz for both cases. A well-defined boundary of the diffused and pristine region is clearly visible in the FIG. 2 and the modified region does not show any major clustering of ions or particle inhomogeneities.

[0125] Further analysis of the diffusion characteristics of each ions in silica was carried out using high angle angular dark field (HAADF) elemental mapping of sample B. FIG. 3 depicts a 4001600 nm HAADF slices of individual elements. A line intensity profile shows the relative concentration profile of each diffused elements with a well-defined and sharp boundary within the silica. The oxygen concentration in silica remained unchanged across the boundary while silicon showed a complementary concentration profile with respect to the diffused elements. This indicates the formation of a complex alloy glass of silica with implanted ions increasing refractive index from 1.457 of that of silica to 1.626. The atomic concentration of silicon in the diffused region is determined to be 57% while Te, Zn, Na and Er constitute the rest in Sample A. This confirms a single step multi-ion diffusion process in the silica glass substrate. The diffusion is highly uniform and homogenous along the transverse and horizontal sections of the silica substrate.

Structural Properties of Diffused Region:

[0126] Silica and tellurite are completely immiscible and will not form a stable glass under conventional batch melting and quenching process. However in the results presented above it is demonstrated that diffusion of metal ions including Te4+ ions in to the silica glass network is possible. The properties of the implanted silica glass were measured. No signals of any kind of crystallization were observed in electron diffraction and XRD characterization proving a complete amorphous phase of silica-tellurite glass. Raman spectroscopy was used to analyse the glass network in the diffused region. FIG. 4 represent the Raman spectrum of ion diffused glass compared with bare silica and tellurite bulk glass. The TZN bulk glass shows typical raman spectrum with peaks at 817 cm.sup.1 (TeO.sub.3+1 and TeO.sub.3 stretching), 653 cm.sup.1 (TeO.sub.4 stretching) and 520 cm.sup.1 (TeOTe bending). On analysing the Raman spectrum of the implanted region on the substrate, a broad peak corresponding to TeO.sub.4 stretching vibrations are found within the range 600-668 cm.sup.1. The reduction in intensity is due to the distortion and destruction of Tea.sub.4 groups. This observation is supplemented by the fact that the 794 cm.sup.1 vibration is increased with the formation of more TeO.sub.3+1 and TeO.sub.3 groups. The 490 cm.sup.1 peak which is very weak in silica substrate shows a strong and sharp response in the implanted glass. This indicates the post-implant state of SiOSi bonds, 490 cm.sup.1 peak in -SiO.sub.2 was experimentally demonstrated to increase its intensity with elastic tensile stress and later explained that this is arising from the four-membered ring structures in -SiO.sub.2. Hence the vibration becomes stronger when their concentration increases upon increase in density of -SiO.sub.2. The broadness in the peak found at 600-668 cm.sup.1 may take up contribution from the reported 604 cm.sup.1 peak in -SiO.sub.2 due to stretched SiO bonds during irradiation process.